1. Field of Invention
The present invention relates to a radio-controlled timepiece that receives a standard time signal containing time information and adjusts the time based on the received standard time signal, and to a control method for the radio-controlled timepiece.
2. Description of Related Art
Radio-controlled timepieces that can receive a standard time signal are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-H10-82874.
The JJY (R) signal transmitted as a standard time signal in Japan is a train of 1-Hz rectangular wave pulses in which a 0.5-second pulse width HIGH signal denotes a 1, a 0.8-second pulse width HIGH signal denotes a 0, and a 0.2-second pulse width HIGH signal denotes a position marker (P). JP-A-H10-82874 teaches a method of sampling the JJY signal by deleting the first 0.2-second portion of the high signal level that is common to all signal pulses and deleting the final 0.2-second low level portion that is also common to all signal pulses.
JP-A-H10-82874 enables eliminating the effects of noise that may be contained in these common parts of each signal by sampling and decoding the received signal using only the portion of each signal where the signal level is different.
However, because JP-A-H10-82874 only teaches adjusting the pulse detection period, sufficient reception performance cannot be achieved when the S/N ratio is low, such as when the reception level is low.
One conceivable way to enable receiving the standard time signal even when the S/N ratio is low is to increase the operating power of the reception circuit to improve the S/N ratio.
However, current consumption also rises if the operating current is increased, thus particularly shortening the duration time in devices such as a wristwatch with low battery capacity.